Methods and devices comprising soluble conjugated polymers

ABSTRACT

Methods, compositions and articles of manufacture involving soluble conjugated polymers are provided. The conjugated polymers have a sufficient density of polar substituents to render them soluble in a polar medium, for example water and/or methanol. The conjugated polymer may desirably comprise monomers which alter its conductivity properties. In some embodiments, the inventors have provided cationic conjugated polymers (CCPs) comprising both solubilizing groups and conductive groups, resulting in conductive conjugated polymers soluble in polar media. The different solubility properties of these polymers allow their deposition in solution in multilayer formats with other conjugated polymers. Also provided are articles of manufacture comprising multiple layers of conjugated polymers having differing solubility characteristics. Embodiments of the invention are described further herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Work leading to this invention was performed under support from the AirForce Office of Scientific Research and under support from theUniversity of California under the UC SMART Program. The U.S. Governmentmay have limited rights in this invention.

TECHNICAL FIELD

This invention relates to soluble conjugated polymers.

BACKGROUND OF THE INVENTION

Polymeric semiconductors have been incorporated into a wide array ofelectronic, optical and optoelectronic materials and devices. Onelimitation on manufacturing processes involving semiconducting polymersis the difficulties in preparing multilayer materials. Solutionprocessing is one of the simplest, most economical, and mostcontrollable methods for depositing layers of a conjugated polymer ofinterest. However, because most conjugated polymers are soluble inorganic and/or nonpolar media, depositing a solution of one conjugatedpolymer onto a previously deposited layer of another conjugated polymercan solubilize it and result in interfacial mixing. This can lead todisruption of the desired device orientation/structure/geometry, processirreproducibility, and reduced efficiency of resulting devices. Thustraditional manufacturing methods for multilayer devices typicallyinvolve only one solution processing step for depositing polymers, withremaining layers deposited by more problematic methods, includingsputtering, thermal vapor deposition, and chemical deposition methods,which can be more costly and less controllable.

There is a need in the art for conjugated polymers having differentphysical properties, for methods of making and using them, and forcompositions, articles of manufacture and machines comprising suchcompounds.

SUMMARY OF THE INVENTION

Methods, compositions and articles of manufacture involving solubleconjugated polymers are provided. The conjugated polymers have asufficient density of polar substituents to render them soluble in apolar medium, for example water and/or methanol. The conjugated polymermay desirably comprise monomers which alter its conductivity properties.In some embodiments, the inventors have provided cationic conjugatedpolymers (CCPs) comprising both solubilizing groups and conductivegroups, resulting in conductive conjugated polymers soluble in polarmedia. The different solubility properties of these polymers allow theirdeposition in solution in multilayer formats with other conjugatedpolymers. Also provided are articles of manufacture comprising multiplelayers of conjugated polymers having differing solubilitycharacteristics. Embodiments of the invention are described furtherherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the HOMO (highest occupied molecular orbital) and LUMO(lowest unoccupied molecular orbital) energy levels ofpoly(9,9-dioctylfluorenyl-2,7-diyl (“PFO”),poly(9,9-dihexyl-fluorene-co-benzothiadiazole) (“PFO-BT”),poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (“MEH-PPV”)andpoly{[9,9-bis(6′-(N,N,N-trimethylammonium)hexyl)fluorine-2,7-diyl]-alt-[2,5-bis(p-phenylene)-1,3,4-oxadiazole]}(“PFON⁺(CH3)₃I⁻-PBD”)compared to the work function of Ba (all referenced with respect to thevacuum).

FIG. 2 shows the current density (mA/cm²) vs. applied voltage (V) andluminance (cd/m²) vs. applied voltage (V) for devices made usingblue-emitting PFO with and without PFON⁺(CH₃)₃I⁻-PBD as anelectron-transport layer (ETL).

FIG. 3 shows the luminous efficiency (cd/A) as a function of currentdensity (mA/cm²) for devices made with (a) PFO, (b) PFO-BT and (c)MEH-PPV with and without ETL. Insets: (a) Power efficiency (lm/W) vs.bias (V) for devices made by PFO with and without ETL; (b) and (c)brightness (cd/m²) vs. current density (mA/cm²) for devices made byPFO-BT and MEH-PPV with and without ETL, respectively.

FIGS. 4 (a) and (b) are atomic force microscope (AFM) images show thesurface of the ETL and that of the emissive polymer. The ETL layerprovides an increased amount of features on the scale shown, providingmore effective electron injection is achieved simply because of theincreased contact area between ETL and cathode.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have provided conjugated polymers having desirableproperties. The conjugated polymers have a sufficient density of polarsubstituents to render them soluble in a polar medium. The polymers thushave desirable solubility properties allowing for their use withpolymers of differing solubilities in methods involving multiplesolution processing steps. The different solubility properties of thesepolymers allow their deposition in solution in multilayer formats withother conjugated polymers.

In some embodiments, the polar substituents can be charged groups, forexample cationic or anionic groups. The conjugated polymers may have asufficient density of solubilizing polar groups to render them solublein a highly polar solvent such as water and/or methanol. This can beparticularly advantageous for preparing multilayer polymeric devices vianovel solution processing methods, also provided.

The conjugated polymer may desirably comprise monomers which alter itsconductivity properties. The conjugated polymer can comprise monomerswhich improve its ability to inject and/or transport electrons. Theconjugated polymer can comprise monomers which improve its ability toinject and/or transport holes. The conductivity of such polymers can becontrolled through the type and/or amount of monomer(s) used, which maybe selected to match with other materials of interest in electronicdevices. The composition of the polymer may also be chosen to preventconductivity of certain species. For example, the composition of thepolymer may be chosen so that it has hole-blocking properties, which canbe desirable in certain device configurations, for example in polymerlight-emitting diodes (PLEDs).

In some embodiments, the inventors have provided cationic conjugatedpolymers (CCPs) comprising both solubilizing groups and conductivegroups, resulting in conductive conjugated polymers soluble in polarmedia. These conductive polymers are desirably soluble in water and/orlower alcohols, particularly methanol.

In some embodiments the CCPs can comprising monomers which perturb thepolymer's ability to form rigid-rod structures, allowing them to form agreater range of three-dimensional structures. The monomers are aromaticmolecules having attachment points to the adjacent subunits of thepolymer which form an angle of greater than about 25° from linear. Themonomers may introduce a torsional twist in the conjugated polymer,thereby further disrupting the ability of the polymer to form arigid-rod structure.

Also provided are articles of manufacture comprising multiple layers ofconjugated polymers having differing solubility characteristics.Multiple polymer layers produced by methods described herein can beincorporated in any of a variety of articles and machines.

Embodiments of the invention can comprise multiplex formats. Forexample, a plurality of different LEDs can be used simultaneously in adisplay format. Multiplex embodiments may employ 2, 3, 4, 5, 10, 15, 20,25, 50, 100, 200, 400, 1000, 5000, 10000, 50000, 200000, one million ormore distinct articles provided by one or more embodiments describedherein. Other aspects of the invention are discussed further herein.

Before the present invention is described in further detail, it is to beunderstood that this invention is not limited to the particularmethodology, articles, compositions or apparatuses described, as suchmethods, articles, compositions or apparatuses can, of course, vary. Itis also to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto limit the scope of the present invention.

Use of the singular forms “a,” “an,” and “the” include plural referencesunless the context clearly dictates otherwise. Thus, for example,reference to “a conjugated polymer” includes a plurality of conjugatedpolymers, reference to “a solvent” includes a plurality of suchsolvents, reference to “an LED” includes a plurality of LEDs, and thelike. Additionally, use of specific plural references, such as “two,”“three,” etc., read on larger numbers of the same subject unless thecontext clearly dictates otherwise. The term “or” when used herein asthe sole conjunction means “and/or” unless stated otherwise. The term“including” and related terms such as “includes” as used herein are notlimiting and allow for the presence of elements in addition to thosespecifically recited.

Terms such as “connected,” “attached,” and “linked” are usedinterchangeably herein and encompass direct as well as indirectconnection, attachment, linkage or conjugation unless the contextclearly dictates otherwise.

Where a range of values is recited, it is to be understood that eachintervening integer value, and each fraction thereof, between therecited upper and lower limits of that range is also specificallydisclosed, along with each subrange between such values. The upper andlower limits of any range can independently be included in or excludedfrom the range, and all such ranges are encompassed within theinvention. Where a value being discussed has inherent limits, forexample where a component can be present at a concentration of from 0 to100%, or where the pH of an aqueous solution can range from 1 to 14,those inherent limits are specifically disclosed as are ranges based onthose inherent limits. Where a value is explicitly recited, it is to beunderstood that values which are about the same quantity or amount asthe recited value are also within the scope of the invention, as areranges based thereon with any other value as described herein.

Where a combination or group of elements is disclosed, each subset ofthose elements is also specifically disclosed and is within the scope ofthe invention. Conversely, where different elements or groups ofelements are disclosed, combinations thereof are also disclosed.

Where any element of an invention is disclosed as having a plurality ofalternatives, examples of that invention in which each alternative isexcluded singly or in any combination with the other alternatives arealso hereby disclosed; more than one element of an invention can havesuch exclusions, and all combinations of elements having such exclusionsare hereby disclosed.

Unless defined otherwise or the context clearly dictates otherwise, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art to which thisinvention belongs. Although any methods and materials similar orequivalent to those described herein can be used in the practice ortesting of the invention, the preferred methods and materials are nowdescribed.

All publications mentioned herein are hereby incorporated by referencefor the purpose of disclosing and describing the particular materialsand methodologies for which the reference was cited. The publicationsdiscussed herein are provided solely for their disclosure prior to thefiling date of the present application. Nothing herein is to beconstrued as an admission that the invention is not entitled to antedatesuch disclosure by virtue of prior invention.

Definitions

In describing the present invention, the following terms will beemployed, and are intended to be defined as indicated below.

“Alkyl” refers to a branched, unbranched or cyclic saturated hydrocarbongroup of 1 to 24 carbon atoms optionally substituted at one or morepositions, and includes polycyclic compounds. Examples of alkyl groupsinclude optionally substituted methyl, ethyl, n-propyl, isopropyl,n-butyl, s-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl,n-heptyl, n-octyl, n-decyl, hexyloctyl, tetradecyl, hexadecyl, eicosyl,tetracosyl and the like, as well as cycloalkyl groups such ascyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, adamantyl, and norbornyl. The term “lower alkyl” refers toan alkyl group of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms.Exemplary substituents on substituted alkyl groups include hydroxyl,cyano, alkoxy, ═O, ═S, —NO₂, halogen, haloalkyl, heteroalkyl,carboxyalkyl, amine, amide, thioether and —SH.

“Alkoxy” refers to an “—Oalkyl” group, where alkyl is as defined above.A “lower alkoxy” group intends an alkoxy group containing one to six,more preferably one to four, carbon atoms.

“Alkenyl” refers to an unsaturated branched, unbranched or cyclichydrocarbon group of 2 to 24 carbon atoms containing at least onecarbon-carbon double bond and optionally substituted at one or morepositions. Examples of alkenyl groups include ethenyl, 1-propenyl,2-propenyl (allyl), 1-methylvinyl, cyclopropenyl, 1-butenyl, 2-butenyl,isobutenyl, 1,4-butadienyl, cyclobutenyl, 1-methylbut-2-enyl,2-methylbut-2-en-4-yl, prenyl, pent-1-enyl, pent-3-enyl,1,1-dimethylallyl, cyclopentenyl, hex-2-enyl, 1-methyl-1-ethylallyl,cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, decenyl,tetradecenyl, hexadecenyl, eicosenyl, tetracosenyl and the like.Preferred alkenyl groups herein contain 2 to 12 carbon atoms. The term“lower alkenyl” intends an alkenyl group of 2 to 6 carbon atoms,preferably 2 to 4 carbon atoms. The term “cycloalkenyl” intends a cyclicalkenyl group of 3 to 8, preferably 5 or 6, carbon atoms. Exemplarysubstituents on substituted alkenyl groups include hydroxyl, cyano,alkoxy, ═O, ═S, —NO₂, halogen, haloalkyl, heteroalkyl, amine, thioetherand —SH.

“Alkenyloxy” refers to an “—Oalkenyl” group, wherein alkenyl is asdefined above.

“Alkylaryl” refers to an alkyl group that is covalently joined to anaryl group. Preferably, the alkyl is a lower allyl. Exemplary alkylarylgroups include benzyl, phenethyl, phenopropyl, 1-benzylethyl,phenobutyl, 2-benzylpropyl and the like.

“Alkylaryloxy” refers to an “—Oalkylaryl” group, where alkylaryl is asdefined above.

“Alkynyl” refers to an unsaturated branched or unbranched hydrocarbongroup of 2 to 24 carbon atoms containing at least one —C≡C— triple bond,optionally substituted at one or more positions. Examples of alkynylgroups include ethynyl, n-propynyl, isopropynyl, propargyl, but-2-ynyl,3-methylbut-1-ynyl, octynyl, decynyl and the like. Preferred alkynylgroups herein contain 2 to 12 carbon atoms. The term “lower alkynyl”intends an alkynyl group of 2 to 6, preferably 2 to 4, carbon atoms, andone —C≡C— triple bond. Exemplary substituents on substituted alkynylgroups include hydroxyl, cyano, alkoxy, ═O, ═S, —NO₂, halogen,haloalkyl, heteroalkyl, amine, thioether and —SH.

“Amide” refers to —C(O)NR′R″, where R′ and R″ are independently selectedfrom hydrogen, alkyl, aryl, and alkylaryl.

“Amine” refers to an —N(R′)R″ group, where R′ and R″ are independentlyselected from hydrogen, alkyl, aryl, and alkylaryl.

“Aryl” refers to an aromatic group that has at least one ring having aconjugated pi electron system and includes carbocyclic, heterocyclic,bridged and/or polycyclic aryl groups, and can be optionally substitutedat one or more positions. Typical aryl groups contain 1 to 5 aromaticrings, which may be fused and/or linked. Exemplary aryl groups includephenyl, furanyl, azolyl, thiofuranyl, pyridyl, pyrimidyl, pyrazinyl,triazinyl, biphenyl, indenyl, benzofuranyl, indolyl, naphthyl,quinolinyl, isoquinolinyl, quinazolinyl, pyridopyridinyl,pyrrolopyridinyl, purinyl, tetralinyl and the like. Exemplarysubstituents on optionally substituted aryl groups include alkyl,alkoxy, alkylcarboxy, alkenyl, alkenyloxy, alkenylcarboxy, aryl,aryloxy, alkylaryl, alkylaryloxy, fused saturated or unsaturatedoptionally substituted rings, halogen, haloalkyl, heteroalkyl, —S(O)R,sulfonyl, —SO₃R, —SR, —NO₂, —NRR′, —OH, —CN, —C(O)R, —OC(O)R, —NHC(O)R,—(CH₂)_(n)CO₂R or —(CH₂)_(n)CONRR′ where n is 0-4, and wherein R and R′are independently H, alkyl, aryl or alkylaryl.

“Aryloxy” refers to an “—Oaryl” group, where aryl is as defined above.

“Carbocyclic” refers to an optionally substituted compound containing atleast one ring and wherein all ring atoms are carbon, and can besaturated or unsaturated.

“Carbocyclic aryl” refers to an optionally substituted aryl groupwherein the ring atoms are carbon.

“Halo” or “halogen” refers to fluoro, chloro, bromo or iodo. “Halide”refers to the anionic form of the halogens.

“Haloalkyl” refers to an alkyl group substituted at one or morepositions with a halogen, and includes alkyl groups substituted withonly one type of halogen atom as well as alkyl groups substituted with amixture of different types of halogen atoms. Exemplary haloalkyl groupsinclude trihalomethyl groups, for example trifluoromethyl.

“Heteroalkyl” refers to an alkyl group wherein one or more carbon atomsand associated hydrogen atom(s) are replaced by an optionallysubstituted heteroatom, and includes alkyl groups substituted with onlyone type of heteroatom as well as alkyl groups substituted with amixture of different types of heteroatoms. Heteroatoms include oxygen,sulfur, and nitrogen. As used herein, nitrogen heteroatoms and sulfurheteroatoms include any oxidized form of nitrogen and sulfur, and anyform of nitrogen having four covalent bonds including protonated andalkylated forms. An optionally substituted heteroatom refers to aheteroatom having one or more attached hydrogens optionally replacedwith alkyl, aryl, alkylaryl and/or hydroxyl.

“Heterocyclic” refers to a compound containing at least one saturated orunsaturated ring having at least one heteroatom and optionallysubstituted at one or more positions. Typical heterocyclic groupscontain 1 to 5 rings, which may be fused and/or linked, where the ringseach contain five or six atoms. Examples of heterocyclic groups includepiperidinyl, morpholinyl and pyrrolidinyl. Exemplary substituents foroptionally substituted heterocyclic groups are as for alkyl and aryl atring carbons and as for heteroalkyl at heteroatoms.

“Heterocyclic aryl” refers to an aryl group having at least 1 heteroatomin at least one aromatic ring. Exemplary heterocyclic aryl groupsinclude furanyl, thienyl, pyridyl, pyridazinyl, pyrrolyl, N-loweralkyl-pyrrolo, pyrimidyl, pyrazinyl, triazinyl, tetrazinyl, triazolyl,tetrazolyl, imidazolyl, bipyridyl, tripyridyl, tetrapyridyl, phenazinyl,phenanthrolinyl, purinyl and the like.

“Hydrocarbyl” refers to hydrocarbyl substituents containing 1 to about20 carbon atoms, including branched, unbranched and cyclic species aswell as saturated and unsaturated species, for example alkyl groups,alkylidenyl groups, alkenyl groups, alkylaryl groups, aryl groups, andthe like. The term “lower hydrocarbyl” intends a hydrocarbyl group ofone to six carbon atoms, preferably one to four carbon atoms.

A “substituent” refers to a group that replaces one or more hydrogensattached to a carbon or nitrogen. Exemplary substituents include alkyl,alkylidenyl, alkylcarboxy, alkoxy, alkenyl, alkenylcarboxy, alkenyloxy,aryl, aryloxy, alkylaryl, alkylaryloxy, —OH, amide, carboxamide,carboxy, sulfonyl, ═O, ═S, —NO₂, halogen, haloalkyl, fused saturated orunsaturated optionally substituted rings, —S(O)R, —SO₃R, —SR, —NRR′,—OH, —CN, —C(O)R, —OC(O)R, —NHC(O)R, —(CH₂)_(n)CO₂R or —(CH₂)_(n)CONRR′where n is 0-4, and wherein R and R′ are independently H, alkyl, aryl oralkylaryl. Substituents also include replacement of a carbon atom andone or more associated hydrogen atoms with an optionally substitutedheteroatom.

“Sulfonyl” refers to —S(O)₂R, where R is alkyl, aryl, —C(CN)═C-aryl,—CH₂CN, alkylaryl, or amine.

“Tioamide” refers to —C(S)NR′R″, where R′ and R″ are independentlyselected from hydrogen, alkyl, aryl, and alkylaryl.

“Thioether” refers to —SR, where R is alkyl, aryl, or alkylaryl.

“Multiplexing” herein refers to an assay or other analytical method inwhich multiple analytes can be assayed simultaneously.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs singly or multiply andinstances where it does not occur at all. For example, the phrase“optionally substituted alkyl” means an alkyl moiety that may or may notbe substituted and the description includes both unsubstituted,monosubstituted, and polysubstituted alkyls.

Conjugated Polymer Soluble in Polar Media

Conjugated polymers (CPs) soluble in polar media are provided and can beused in embodiments described herein. The CPs comprise polar groups assolubilizing functionalities linked to polymer subunits to increasepolymer solubility in polar media. Any or all of the subunits of the CPmay comprise one or more pendant solubilizing groups. Exemplary polargroups include those introducing one or more dipole moments to the CP,for example halides, hydroxyls, amines, amides, cyano, carboxylic acids,and thiols.

Preferably the polar groups are charged groups, more preferably cationicgroups. Any suitable cationic groups may be incorporated into CCPs.Exemplary cationic groups which may be incorporated include ammoniumgroups, guanidinium groups, histidines, polyamines, pyridinium groups,and sulfonium groups.

The solubilizing functionality may be linked to the conjugated polymerbackbone by a linker, preferably an unconjugated linker, for examplealkyl groups, polyethers, alkylamines, and/or polyamines.

One synthetic approach to introducing a charged group into a conjugatedpolymer is as follows. A neutral polymer is first formed by the Suzukicoupling of one or more bis- (or tris- etc.) boronic acid-substitutedmonomer(s) with one or more monomers that have at least two brominesubstitutions on aromatic ring positions. Bromine groups are attached toany or all of the monomers via linkers. Conversion to cationicwater-soluble polymers is accomplished by addition of condensedtrimethylamine, which replaces the pendant bromines with ammoniumgroups.

In some embodiments, the conjugated polymer may desirably compriseconductive monomers which alter the conductivity of the overall polymer,increasing its ability to transport an electrical species. For example,the conjugated polymer can comprise monomer(s) which improve its abilityto inject and/or transport electrons. The conjugated polymer cancomprise monomer(s) which improve its ability to inject and/or transportholes. More than one type of conductive monomer can be incorporated inthe conjugated polymer. The conductivity of such polymers can becontrolled through the type and/or amount of monomer(s) used, which canbe selected to provide an electronic configuration compatible with othermaterials of interest in a given electronic device.

The conductive monomers may be electron-deficient monomers orelectron-rich monomers. Electron-deficient monomers can be used toincrease the ability of the polymer to inject and/or transportelectrons, and to improve its ability to serve as an electron-transportlayer. Electron-deficient monomers include unsaturated and/or aromaticgroups appropriately substituted with electron-withdrawing groups. Anumber of electron-deficient monomers are known in the art. Exemplaryelectron-deficient monomers include benzothiadiazole, oxadiazole,quinoxaline, cyano-substituted olefins, squaric acid, and maleimide.

Electron-rich monomers can be used to increase the ability of thepolymer to inject and/or transport holes, and to improve its ability toserve as a hole-transport layer. Electron-rich monomers includeunsaturated and/or aromatic groups appropriately substituted withelectron-donating groups, for example alkyl groups. A number ofelectron-rich monomers are known in the art. Exemplary electron-richmonomers include 9,9-dialkylfluorenes, 2,5-dimethyl-1,4-phenylidene,2,5-dioctyloxy-1,4-phenylidene, and terthiophenes.

The composition of the polymer can also be chosen to preventconductivity of certain species. For example, the composition of thepolymer can be chosen so that it has hole-blocking properties, which canbe desirable in certain device configurations, for example in polymerlight-emitting diodes (PLEDs).

In some embodiments the polymers can comprise angled linkers with asubstitution pattern (or regiochemistry) capable of perturbing thepolymers' ability to form rigid-rod structures, allowing them to have agreater range of three-dimensional structures. The polymers can compriseat least three subunits with at least one angled linker, which may beinternal and/or an end unit, and may comprise at least 4, 5, 6, 8, 10,15, 20, 25 or more subunits. The polymers may comprise up to about 100,200, 300, 500, 1000, 2000, 5000, 10000, 20000, 50000 or more subunits.

The angled linker(s) are optionally substituted aromatic moleculeshaving at least two separate bonds to other polymer components (e.g.,monomers, block polymers, end groups) that are capable of forming anglesrelative to one another which disrupt the overall ability of the polymerto form an extended rigid-rod structure (although significant regionsexhibiting such structure may remain.) The angled linkers may bebivalent or polyvalent.

The angle which the angled linkers are capable of imparting to thepolymeric structure is determined as follows. Where the two bonds toother polymeric components are coplanar, the angle can be determined byextending lines representing those bonds to the point at which theyintersect, and then measuring the angle between them. Where the twobonds to other polymeric components are not coplanar, the angle can bedetermined as follows: a first line is drawn between the two ring atomsto which the bonds attach; two bond lines are drawn, one extending fromeach ring atom in the direction of its respective bond to the otherpolymeric component to which it is joined; the angle between each bondline and the first line is fixed; and the two ring atoms are then mergedinto a single point by shrinking the first line to a zero length; theangle then resulting between the two bond lines is the angle the angledlinker imparts to the polymer.

The angle which an angled linker is capable of imparting to the polymeris typically less than about 155°, and may be less than about 150°, lessthan about 145°, less than about 140°, less than about 135°, less thanabout 130°, less than about 125°, less than about 120°, less than about115°, less than about 110°, less than about 105°, less than about 100°,less than about 95°, less than about 90°, less than about 85°, less thanabout 80°, less than about 75°, less than about 70°, less than about65°, less than about 60°, less than about 55°, or less than about 50°.The angled linker may form an angle to its adjacent polymeric units ofabout 25°, 30°, 35°, 40°, 45°, 50°, 60° or more. The angled linker mayintroduce a torsional twist in the conjugated polymer, thereby furtherdisrupting the ability of the polymer to form a rigid-rod structure. Forangled linkers having an internally rotatable bond, such aspolysubstituted biphenyl, the angled linker must be capable of impartingan angle of less than about 155° in at least one orientation.

For six-membered rings, such angles can be achieved through ortho ormeta linkages to the rest of the polymer. For five-membered rings,adjacent linkages fall within this range. For eight-membered rings,linkages extending from adjacent ring atoms, from alternate ring atoms(separated by one ring atom), and from ring atoms separated by two otherring atoms fall within this range. Ring systems with more than eightring atoms may be used. For polycyclic structures, even more diverselinkage angles can be achieved.

Exemplary linking units which meet these limitations include benzenederivatives incorporated into the polymer in the 1, 2 or 1,3-positions;naphthalene derivatives incorporated into the polymer in the 1,2-, 1,3-,1,6-, 1,7-, 1,8-positions; anthracene derivatives incorporated into thepolymer in the 1,2-, 1,3-, 1,6-, 1,7-, 1,8-, and 1,9-positions; biphenylderivatives incorporated into the polymer in the 2,3-, 2,4-, 2,6-,3,3′-, 3,4-, 3,5-, 2,2′-, 2,3′-, 2,4′-, and 3,4′-positions; andcorresponding heterocycles. The position numbers are given withreference to unsubstituted carbon-based rings, but the same relativepositions of incorporation in the polymer are encompassed in substitutedrings and/or heterocycles should their distribution of substituentschange the ring numbering.

The CP can be a copolymer, and may be a block copolymer, a graftcopolymer, or both. The solubilizing functionalities, the conductivesubunits and/or the angled linkers may be incorporated into the CPrandomly, alternately, periodically and/or in blocks.

Exemplary polymers which may form the backbone of the compounds of thepresent invention include, for example, polypyrroles, polyfluorenes,polyphenylene-vinylenes, polythiophenes, polyisothianaphthenes,polyanilines, poly-p-phenylenes and copolymers thereof. Other exemplarypolymeric subunits and repeating units are shown in the accompanyingtables.

TABLE 1 Typical aromatic repeat units for the construction of conjugatedsegments and oligomeric structures.

TABLE 2 Examples of conjugated segments and oligomeric structures of CP

The CP contains a sufficient density of solubilizing functionalities torender the overall polymer soluble in a polar medium. The CP preferablycontains at least about 0.01 mol % of the monomers substituted with atleast one solubilizing functionality, and may contain at least about0.02 mol %, at least about 0.05 mol %, at least about 0.1 mol %, atleast about 0.2 mol %, at least about 0.5 mol %, at least about 1 mol %,at least about 2 mol %, at least about 5 mol %, at least about 10 mol %,at least about 20 mol %, or at least about 30 mol %. The CP may containup to 100 mol % of the solubilizing functionality, and may contain about99 mol % or less, about 90 mol % or less, about 80 mol % or less, about70 mol % or less, about 60 mol % or less, about 50 mol % or less, orabout 40 mol % or less.

The CP preferably contains at least about 0.01 mol % of the conductivemonomers, and may contain at least about 0.02 mol %, at least about 0.05mol %, at least about 0.1 mol %, at least about 0.2 mol %, at leastabout 0.5 mol %, at least about 1 mol %, at least about 2 mol %, atleast about 5 mol %, at least about 10 mol %, at least about 20 mol %,or at least about 30 mol %. The CP may contain up to 100 mol % of theconductive monomers, and may contain about 99 mol % or less, about 90mol % or less, about 80 mol % or less, about 70 mol % or less, about 60mol % or less, about 50 mol % or less, or about 40 mol % or less.

The polymer may contain at least about 0.01 mol % of the angled linker,and may contain at least about 0.02 mol %, at least about 0.05 mol %, atleast about 0.1 mol %, at least about 0.2 mol %, at least about 0.5 mol%, at least about 1 mol %, at least about 2 mol %, at least about 5 mol%, at least about 10 mol %, at least about 20 mol %, or at least about30 mol %. The polymer may contain up to 100 mol % of the angled linker,and may contain about 99 mol % or less, about 90 mol % or less, about 80mol % or less, about 70 mol % or less, about 60 mol % or less, about 50mol % or less, or about 40 mol % or less.

Desirably, the CPs described herein are soluble in aqueous solutions andother highly polar solvents, and preferably are soluble in water. By“water-soluble” is meant that the material exhibits solubility in apredominantly aqueous solution, which, although comprising more than 50%by volume of water, does not exclude other substances from thatsolution, including without limitation buffers, blocking agents,cosolvents, salts, metal ions and detergents.

In one embodiment, an exemplary CCP is represented by Formula A:

wherein:

CP₁, CP₂, CP₃, and CP₄ are optionally substituted conjugated polymersegments or oligomeric structures, and may be the same or different fromone another. CP₁, CP₂, CP₃, and CP₄ may be aromatic repeat units, andmay be selected from the group consisting of benzene, naphthalene,anthracene, fluorene, thiophene, furan, pyridine, and oxadiazole, eachoptionally substituted. Typical aromatic repeat units are shown in Table1 below, and representative polymeric segments and oligomeric structuresare shown in Table 2. One or more of CP₁₋₄ may be conductive monomerscomprising electron-injecting and/or transporting properties orhole-injecting and/or transporting properties. The conductive monomersmay be evenly or randomly distributed along the polymer main chain.

CP₁, CP₂, CP₃ and CP₄ are each optionally substituted at one or morepositions with one or more groups selected from -R₁-A, -R₂-B, -R₃-C and-R₄-D, which may be attached through bridging functional groups -E- and—F—, with the proviso that the polymer as a whole must be substitutedwith a plurality of cationic groups.

R₁, R₂, R₃ and R₄ are independently selected from alkyl, alkenyl,alkoxy, alkynyl, and aryl, alkylaryl, arylalkyl, and polyalkylene oxide,each optionally substituted, which may contain one or more heteroatoms,or may be not present. R₁, R₂, R₃ and R₄ can be independently selectedfrom C₁₋₂₂ alkyl, C₁₋₂₂ alkoxy, C₁₋₂₂ ester, polyalkylene oxide havingfrom 1 to about 22 carbon atoms, cyclic crown ether having from 1 toabout 22 carbon atoms, or not present. Preferably, R₁, R₂, R₃ and R₄ maybe selected from straight or branched alkyl groups having 1 to about 12carbon atoms, or alkoxy groups with 1 to about 12 carbon atoms. It is tobe understood that more than one functional group may be appended to therings as indicated in the formulas at one or more positions.

A, B, C and D are independently selected from H, —SiR′R″R′″, —N⁺R′R″R′″,a guanidinium group, histidine, a polyamine, a pyridinium group, and asulfonium group. R′, R″ and R′″ are independently selected from thegroup consisting of hydrogen, C₁₋₁₂ alkyl and C₁₋₁₂ alkoxy and C₃₋₁₀cycloalkyl. It is preferred that R′, R″ and R′″ are lower alkyl or loweralkoxy groups.

E and F are independently selected from not present, —O—, —S—, —C(O)—,—C(O)O—, —C(R)(R′)—, —N(R′)—, and —Si(R′)(R″), wherein R′ and R″ are asdefined above.

X is O, S, Se, —N(R′)— or —C(R′)(R″)—, and Y and Z are independentlyselected from —C(R)═ and —N═, where R, R′ and R″ are as defined above.

m and n are independently 0 to about 10,000, wherein m+n>1. Preferably mand n are each independently 0 to about 20 and more preferably from 0 toabout 10. Each repeat of m and n may be the same as or different thanthe other repeats.

a, b, c and d are independently 0 to about 250. At least one of a, b, cand d must be greater than or equal to one.

G and G1 are capping units and may be the same or different. The cappingunits may be activated units that allow further chemical reaction toextend the polymer chain, or may be nonactivated termination units. Gand G1 can be independently selected from hydrogen, optionallysubstituted aryl, halogen substituted aryl, boronic acid substitutedaryl, and boronate radical substituted aryl.

Conjugated polymers may also be provided in purified form. Any availablemethod or combination of methods may be used for purification. Exemplarymethods include precipitation, extraction, and sublimation. Solutions ofthe CP are also provided. Solutions may be provided in a container ofany suitable form. Solutions may be packaged in a container designed forincorporation into a solution processing apparatus, for example aprinter. In some embodiments, the solution may be provided in an inkjetcartridge designed to be used with an inkjet printer.

The Polar Solvent

The conjugated polymer is soluble in a polar medium, a medium comprisingat least one polar solvent. By “polar” is meant having a net dipolemoment. Exemplary polar solvents include dimethylsulfoxide,dimethylformamide, formic acid, acetic acid, ethyl acetate, water,alcohols and polyalcohols, particularly lower alcohols (C₁₋₄),particularly methanol. Preferably the polar solvent has a polarity of atleast that of ethanol or ethyl acetate. In some embodiments, the polarsolvent used to dissolve the CP is selected based on its inability todissolve a second conjugated polymer onto which the CP is to bedeposited.

The polar solvent in certain embodiments and solution formed therefromin some embodiments is wettable on the surface to which it is to beapplied, such that when it is deposited it flows generally uniformly andevenly over the surface, and preferably is controllable in thickness.Combinations of solvents may also be used. Preferably the solvent issufficiently wettable on the substrate that the solution spreadsappropriately when deposited thereon. One or more wetting agents may beincluded in the solution to improve its ability to wet a surface and/orlowers its surface tension. For example, a solution comprising water mayhave an alcohol, a surfactant, or a combination of materials addedthereto serving as wetting agents.

Methods of Use

The CPs described herein can be used in a variety of methods. Methods ofparticular interest include deposition of the CPs into electronicdevices, particularly in devices comprising multiple layers ofconjugated polymers. Any of a variety of deposition methods can be usedin a given device, including without limitation vacuum sputtering (RF orMagnetron), electron beam evaporation, thermal vapor deposition,chemical deposition, sublimation, and solution processing methods. Anydeposition method known or discoverable in the art can be used todeposit the soluble polar polymers provided herein, although solutionmethods are currently preferred.

These layers are commonly deposited by spin-coating, drop-casting,sequential spin-casting, formation of Langinuir-Blodgett films orelectrostatic adsorption techniques.^([28]) Articles of manufacture maybe fabricated by stepwise deposition of polymer layers; the watersolubility of flexible CPs provided herein allows for the sequentialdeposition of layers of different materials with different solubilities,providing certain advantages during manufacturing, including for thedeposition of thin layers of material.

In particular embodiments, solution processing methods can be used toincorporate CPs into an article of manufacture. Printing techniques mayadvantageously be used to deposit the CPs, e.g., inkjet printing, offsetprinting, etc.

Where the CPs are used in multilayer devices comprising multipleconjugated polymeric layers, one or more of these layers may comprisenonpolar conjugated polymers which may not be soluble in a polar mediumof interest. These include, for example, MEH-PPV, P3ATs[poly(3-alkylthiophenes), where alkyl is from 6 to 16 carbons], such aspoly(2,5-dimethoxy-p-phenylene vinylene)-“PDMPV”, andpoly(2,5-thienylenevinylene); poly(phenylenevinylene) or “PPV” andalkoxy derivatives thereof; PFO, PFO-BT, and polyanilines. The nonpolarconjugated polymer can be deposited by any suitable technique; in someembodiments it is deposited or cast directly from solution. Typically,organic solvents are used, typically with low polarity. Exemplaryorganic solvents include: halohydrocarbons such as methylene chloride,chloroform, and carbon tetrachloride; aromatic hydrocarbons such asxylene, benzene, toluene; and other hydrocarbons including decaline.

Mixed solvents can also be used. The differing solubility properties ofnonpolar and polar polymers allow for deposition of multiple polymericlayers via solution processing methods, which can simplify manufacturingand reduce costs. The water-soluble polymers described herein allow forthe solution deposition of alternating layers of polymers of differingsolubilities to form bilayer or multilayer devices.

When depositing the conjugated polymer on a substrate, the solution canbe relatively dilute, such as from 0.1 to 20% w/w in concentration,especially 0.2 to 5% w. In some embodiments, film thicknesses may be atleast about 50, 100, or 200 nm. In some embodiments, film thicknesses ofless than about 400, 200, or 100 nm can be used.

The polymer solution can be formed into a selected shape if desired,e.g. a fiber, film or the like by any suitable method, for exampleextrusion.

After deposition of a solution comprising a conjugated polymer, thesolvent is removed. Any available method or combination of methods maybe used for removing the solvent. Exemplary solvent removal methodsinclude evaporation, heating, extraction, and subjecting the solution toa vacuum.

In some embodiments, the conjugated polymer may be deposited on asubstrate. The substrate can comprise a wide range of material, eitherbiological, nonbiological, organic, inorganic, or a combination of anyof these. In some embodiments, the substrate can be transparent. Thesubstrate can be a rigid material, for example a rigid plastic or arigid inorganic oxide. The substrate can be a flexible material, forexample a transparent organic polymer such as polyethyleneterephthalateor a flexible polycarbonate. The substrate can be conductive ornonconductive.

The CPs can be deposited on a substrate in any of a variety of formats.For example, the substrate may be a polymerized Langmuir Blodgett film,functionalized glass, Si, Ge, GaAs, indium doped GaN, GaP, SiC (Nature430:1009, 2004), SiO2, SiN4, semiconductor nanocrystals, modifiedsilicon, or any of a wide variety of gels or polymers such as(poly)tetrafluoroethylene, (poly)vinylidenedifluoride, polystyrene,cross-linked polystyrene, polyacrylic, polylactic acid, polyglycolicacid, poly(lactide coglycolide), polyanhydrides, poly(methylmethacrylate), poly(ethylene-co-vinyl acetate),polyethyleneterephthalate, polysiloxanes, polymeric silica, latexes,dextran polymers, epoxies, polycarbonates, agarose, poly(acrylamide) orcombinations thereof. Conducting polymers and photoconductive materialscan be used. The substrate can take the form of a photodiode, anoptoelectronic sensor such as an optoelectronic semiconductor chip oroptoelectronic thin-film semiconductor, or abiochip.

The CPs may be used in methods which screen the CPs for any property ofinterest. For example, the CPs may be tested for binding to a target,for energy transfer to a chromophore, for increased fluorescentefficiency, for decreased self-quenching, for absorbance wavelength,emission wavelength, conductive properties, ability to inject and/ortransport electrons, ability to block holes, ability to inject and/ortransport holes, and/or work function, etc.

Articles of Manufacture

The CPs can be incorporated into any of various articles of manufactureincluding optoelectronic or electronic devices, biosensors, diodes,including photodiodes and light-emitting diodes (“LEDs”), optoelectronicsemiconductor chips, semiconductor thin-films, and chips, and can beused in array or microarray form. The polymer can be incorporated into apolymeric photoswitch. The polymer can be incorporated into an opticalinterconnect or a transducer to convert a light signal to an electricalimpulse. The CPs can serve as liquid crystal materials. The CPs may beused as electrodes in electrochemical cells, as conductive layers inelectrochromic displays, as field effective transistors, and as Schottkydiodes.

The CPs can be used as lasing materials. Optically pumped laser emissionhas been reported from MEH-PPV in dilute solution in an appropriatesolvent, in direct analogy with conventional dye lasers [D. Moses, Appl.Phys. Lett. 60, 3215 (1992); U.S. Pat. No. 5,237,582]. Semiconductingpolymers in the form of neat undiluted films have been demonstrated asactive luminescent materials in solid state lasers [F. Hide, M. A.Diaz-Garcia, B. J. Schwartz, M. R. Andersson, Q. Pei, and A. J. Heeger,Science 273, 1833 (1996); N. Tessler, G. J. Denton, and R. H. Friend,Nature 382, 695 (1996)]. The use of semiconducting polymers as materialsfor solid state lasers is disclosed in U.S. Pat. No. 5,881,083 issuedMar. 9, 1999 to Diaz-Garcia et al. and titled “Conjugated Polymers asMaterials for Solid State Lasers.” In semiconducting polymers, theemission is at longer wavelengths than the onset of significantabsorption (the Stokes shift) resulting from inter- and intramolecularenergy transfer. Thus there is minimal self-absorption of the emittedradiation [F. Hide et al., Science 273, 1833 (1996)], so self-absorptiondoes not make the materials lossy. Moreover, since the absorption andemission are spectrally separated, pumping the excited state via the πto π* transition does not stimulate emission, and an inverted populationcan be obtained at relatively low pump power.

Light-emitting diodes can be fabricated incorporating one or more layersof CPs, which may serve as conductive layers. Light can be emitted invarious ways, e.g., by using one or more transparent or semitransparentelectrodes, thereby allowing generated light to exit from the device.

The mechanism of operation of a polymer LED requires that carrierinjection be optimized and balanced by matching the electrodes to theelectronic structure of the semiconducting polymer. For optimuminjection, the work function of the anode should lie at approximatelythe top of the valence band, E_(v), (the π-band or highest occupiedmolecular orbital, HOMO) and the work function of the cathode should lieat approximately the bottom of the conduction band, E_(c), (the π*-bandor lowest unoccupied molecular orbital, LUMO).

LED embodiments include hole-injecting and electron-injectingelectrodes. A conductive layer made of a high work function material(above 4.5 eV) may be used as the hole-injecting electrode. Exemplaryhigh work function materials include electronegative metals such as goldor silver, and metal-metal oxide mixtures such as indium-tin oxide. Anelectron-injecting electrode can be fabricated from a low work functionmetal or alloy, typically having a work function below 4.3. Exemplarylow work function materials include indium, calcium, barium andmagnesium. The electrodes can be applied by any suitable method; anumber of methods are known to the art (e.g. evaporated, sputtered, orelectron-beam evaporation).

In some embodiments, polymer light-emitting diodes have been fabricatedusing a semiconducting polymer cast from solution in an organic solventas an emissive layer and a water-soluble (or methanol-soluble)conjugated copolymer as an electron-transport layer (ETL) in the deviceconfiguration: ITO(indium tin oxide)/PEDOT(poly(3,4-ethylenedioxythiophene)/emissive polymer/ETL/Ba/Al. The inventors havesuccessfully fabricated multi-layer PLEDs using a semiconducting polymer(red, green or blue emitting), cast from solution in an organic solvent,as the emissive layer and a water-soluble (or methanol-soluble) cationicconjugated copolymer as electron-transport layer. The resultsdemonstrate that devices with the ETL have significantly lower turn-onvoltage, higher brightness and improved luminous efficiency.

Although the examples demonstrate the use of an electron-transport layerformed from the soluble conductive polymer, any form of conducting layercan be used. Thus, judicious choice of monomers as described herein canresult in polymers with hole-injecting and/or transporting properties,as well as polymers with electron-injecting and/or transportingproperties. The device geometry and deposition order can be selectedbased on the type of conductive polymer being used. More than one typeof conductive polymer can be used in the same multilayer device. Amultilayer device may include more than one layer of electron-injectingconjugated polymers, more than one layer of hole-injecting conjugatedpolymers, or at least one layer of a hole-injecting polymer and at leastone layer of an electron-injecting conjugated polymer.

In PLEDs, the device efficiency is reduced by cathode quenching sincethe recombination zone is typically located near the cathode.^([20]) Theaddition of an ETL moves the recombination zone away from the cathodeand thereby eliminates cathode quenching. In addition, the ETL can serveto block the diffusion of metal atoms, such as barium and calcium, andthereby prevents the generation of quenching centers^([20]) during thecathode deposition process.

In some embodiments, the principal criteria when a soluble conjugatedpolymer is used as an electron transport layer (ETL) in polymerlight-emitting diodes (PLEDs) are the following: (1) The lowestunoccupied molecular orbital (LUMO) of the ETL must be at an energyclose to, or even within the π*-band of the emissive semiconductingpolymer (so electrons can be injected); and (2) The solvent used forcasting the electron injection material must not dissolve the underlyingemissive polymer.

Similarly, the principal criteria for a polymer based hole transportlayer (HTL) for use in polymer light-emitting diodes (PLEDs) is that thehighest occupied molecular orbital (HOMO) of the HTL must be at anenergy close to, or even within the valence band of the emissivesemiconducting polymer.

Solubility considerations can dictate the deposition order of theparticular CPs ans solvents used to produce a desired deviceconfiguration. Any number of layers of CPs with different solubilitiesmay be deposited via solution processing by employing these techniques.

The PLEDs comprising CPs described herein can be incorporated in anyavailable display device, including a full color LED display, a cellphone display, a PDA (personal digital assistant), portable combinationdevices performing multiple functions (phone/PDA/camera/etc.), a flatpanel display including a television or a monitor, a computer monitor, alaptop computer, a computer notepad, and an integrated computer-monitorsystems. The PLEDs may be incorporated in active or passive matrices.

EXAMPLES

The following examples are set forth so as to provide those of ordinaryskill in the art with a complete description of how to make and use thepresent invention, and are not intended to limit the scope of what isregarded as the invention. Efforts have been made to ensure accuracywith respect to numbers used (e.g., amounts, temperature, etc.) but someexperimental error and deviation should be accounted for. Unlessotherwise indicated, parts are parts by weight, temperature is degreecentigrade and pressure is at or near atmospheric, and all materials arecommercially available.

Experimental

In one embodiment, polymer light-emitting diodes (PLEDs) have beenfabricated using a semiconducting polymer cast from solution in anorganic solvent as an emissive layer and a water-soluble (ormethanol-soluble) conjugated copolymer as an electron-transport layer(ETL) in the device configuration: ITO/PEDOT/emissivepolymers/ETL/Ba/Al. The results demonstrate that devices with the ETLhave significantly lower turn-on voltage, higher brightness and improvedluminous efficiency. See figures.

Example 1 Fabrication of PLEDs

The water soluble conjugated copolymer,poly{[9,9-bis(6′-(N,N,N-trimethylammonium)hexyl)-fluorine-2,7-diyl]-alt-[2,5-bis(p-phenylene)-1,3,4-oxadiazole])}(PFON⁺(CH₃)₃I⁻—PBD)was synthesized using the palladium catalyzed Suzuki couplingreaction^([13,14]) and used as an electron transport layer (ETL).Poly(9,9-dihexyl-fluorene-co-benzothiadiazole) (PFO-BT) was alsosynthesized using the Suzuki coupling reaction.^([15])Poly(9,9-dioctyfluorenyl-2,7-diyl) (PFO) andpoly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)were purchased from American Dye Source, Inc. (Canada). The molecularstructures of PFO, PFO-BT, MEH-PPV and PFON⁺(CH₃)₃I⁻—PBD are shownbelow:

The HOMO (highest occupied molecular orbital) and LUMO energy levels areshown in FIG. 1 (the work functions of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) and barium arealso shown for comparison). PEDOT:PSS on indium tin oxide (ITO) was usedas the hole-injecting bilayer electrode. PLEDS were fabricated with andwithout the ETL layer in the following device structures:(ITO)/PEDOT:PSS/Emissive polymer/Ba/Al and (ITO)/PEDOT:PSS/EmissivePolymer/ETL/Ba/Al. Details of device fabrication and testing have beenreported elsewhere; all fabrication steps were carried out inside acontrolled atmosphere dry box under nitrogen atmosphere.^([16,17]) TheETL was deposited on top of the emissive layer by spin-casting fromsolution in methanol (0.6% wt.-%) to form a PFON⁺(CH₃)₃I⁻—PBD layer withthickness of approximately 30 nm and then annealed at 90° C. for 2 hoursto remove residual solvent. Hydrophilic methanol was used as the solvent(rather than water) to achieve better inter-layer wetting whilemaintaining well-defined multi-layers. The term “emissive polymer/ETL”is used to designate devices with an ETL.

Example 2 Characterization of PLEDs Comprising a Water-Soluble CCP

FIG. 2 shows the current density vs. voltage and brightness vs. voltagecharacteristics of devices made using PFO with and without the ETL. ThePFO/ETL devices turned on at ˜3V (the turn-on voltage is defined as thevoltage at the brightness of 0.1 cd/m²), whereas the turn-on voltage isat ˜5V for PFO devices made without the ETL.^([18]) At 6 V, theluminance (L) obtained from the PFO/ETL devices is L=3450 cd/m²,compared to L=30 cd/m² for devices without the ETL.

Similar improvements were observed from the devices made with green andred emitting conjugated polymers. For MEH-PPV/ETL devices, L=5600 cd/m²at 5 V compared to L=3550 cd/m² for similar devices fabricated withoutthe ETL. Therefore, the addition of the ETL results in lower turn-onvoltage and higher brightness.

The dramatic improvement in brightness and the reduced turn-on voltageresult from improved electron injection (there is a good match of theLUMO of the ETL to the π*-band of the emissive polymer(s)) and from thehole blocking capability of the ETL (LUMO energy at −6.24 eV relative tothe vacuum).

The luminous efficiency (LE in cd/A) vs. current density (J in mA/cm²)for devices with and without the ETL are shown in FIGS. 3 a, 3 b and 3c. As shown in FIG. 3, devices with ETL have higher luminous efficiency,higher power efficiency, and correspondingly higher brightness at agiven voltage.

The improvements in LE and PE can be understood in greater detail bycomparing the LUMO energy level of the emissive polymer with that ofPFON⁺(CH₃)₃I⁻—PBD and the work-function of barium (see FIG. 1). Theenergy barrier between the LUMO of PFO and the work function of bariumis ˜0.6 eV. Thus, by adding the PFON⁺(CH₃)₃I⁻—PBD layer as the ETL,electron injection is enhanced.

For PFO-BT and MEH-PPV, there is no energy barrier for electroninjection. However, the hole-blocking feature of the PFON⁺(CH₃)₃I⁻—PBDlayer leads to better balanced electron and hole currents. In addition,the enhanced electron injection can also facilitate holeinjection.^([21]) Therefore, the larger and more nearly balancedelectron and hole currents lead to higher luminous efficiencies in thedevices with the ETL.

Interfacial energetics are known to play an important role in theemission characteristics of organic LEDs.^([22] [23]) By adding the ETLbetween the cathode and the emissive polymer, the contacts at bothinterfaces are improved. Atomic force microscope (AFM) images show thatthe surface of the ETL is more rough than that of the emissive polymer.See FIG. 4. As a result, more effective electron injection is achievedsimply because of the increased contact area between ETL and cathode.

Conclusion

The water- and methanol-soluble conjugated polymer, PFON⁺(CH₃)₃I⁻—PBD,was used as an electron-transporting layer in multi-layer PLEDs. Bycasting the ETL from solution in methanol and the emissive layer fromsolution in an organic solvent, interfacial mixing was avoided. Usingblue, green or red emitting semiconducting polymers as the emissivelayer and PFON⁺(CH₃)₃I⁻—PBD as the ETL, significant improvements inperformance were demonstrated. More importantly, our results indicatethat multi-layer PLEDs can be fabricated by deposition of multiplesolutions.

Although the invention has been described in some detail with referenceto the preferred embodiments, those of skill in the art will realize, inlight of the teachings herein, that certain changes and modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, the invention is limited only by the claims.

REFERENCES

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What is claimed is:
 1. A method of forming adjacent layers of materialson a substrate, comprising: providing a first solution comprising afirst material that is a water-soluble cationic conjugated polymer and afirst solvent, wherein the conjugated polymer comprises polar groups aspendant solubilizing groups covalently bonded to the conjugated polymer;providing a second solution comprising a second material including anemissive semiconducting polymer and a second solvent; depositing a firstlayer of one of said first and second solutions onto a substrate;depositing a second layer of the other of said first and secondsolutions onto the first layer; wherein the material deposited in thefirst layer does not dissolve in the solvent deposited in the secondlayer, and the water-soluble cationic conjugated polymer has a highestoccupied molecular orbital at an energy within the valence band of theemissive semiconducting polymer, or the water-soluble cationicconjugated polymer has a lowest unoccupied molecular orbital at anenergy within the conduction band of the emissive semiconductingpolymer.
 2. The method of claim 1, wherein the first solvent compriseswater.
 3. The method of claim 1, wherein the first solution comprises adetergent.
 4. The method of claim 1, wherein depositing the firstsolution onto the substrate comprises spin-casting.
 5. The method ofclaim 1, wherein the substrate is a film.
 6. The method of claim 1,wherein the substrate is rigid.
 7. A method of adding a polymer layer toa substrate, comprising: providing a first solution of a cationicwater-soluble conjugated polymer in a solvent, wherein the conjugatedpolymer comprises polar groups as pendant solubilizing groups covalentlybonded to the conjugated polymer; providing a substrate comprising anemissive semiconducting polymer not soluble in the solvent; depositingthe first solution on the substrate; wherein the water-soluble cationicconjugated polymer has a highest occupied molecular orbital at an energywithin the valence band of the emissive semiconducting polymer, or thewater-soluble cationic conjugated polymer has a lowest unoccupiedmolecular orbital at an energy within the conduction band of theemissive semiconducting polymer.
 8. The method of claim 7, wherein thesolvent comprises water.
 9. The method of claim 7, wherein depositingthe first solution onto the substrate comprises spin-casting.
 10. Themethod of claim 7, wherein the substrate is a film.
 11. The method ofclaim 7, wherein the substrate is rigid.